Browser-based applications are deployed and managed centrally, and therefore are inexpensive in comparison to client/server applications. Specifically, in contrast to client/server applications, browser-based applications can be accessed ubiquitously from any web-browser, and therefore do not require the maintenance of specialized software on each user's desktop. On the downside, browser applications suffer from performance issues in that responding to client actions may take several network roundtrips to the server. In contrast, client/server applications carry significant computing intelligence on the client, thereby providing significantly better performance.
Round trips (i.e., multiple communications) on the network can take anywhere from a fraction of a millisecond to more than a second, depending on the type of network and the geographic distance between the client and the server. For example, on a campus Local Area Network (LAN), the latency is typically 0.1 ms. As a second example, the latency on a high-speed land line between New York and Tokyo is ˜400 ms. As a third example, the latency between any two terrestrial points on a satellite link is about 1.5 seconds. In light of this, the performance of browser-based applications depends substantially on the number of network roundtrips required to respond to a typical client action. A response that requires 16 round trips would take well over 7 seconds when the client is in Tokyo and the server is in New York. It is therefore desirable to minimize the number of network roundtrips involved in each response of the application to client action.
In general, application developers tend to focus on providing the best functionality in the application, but pay little attention to performance issues. A market therefore exists for technology to optimize the performance of applications a posteriori by examining the request/response interactions between the client and the server. The situation is similar to that of application development, where application developers write software with a view to richness of functionality, leaving it to compilers and optimizing processors to deliver performance afterwards.
With regard to the impact of network latency on application performance, application developers often construct files (e.g., web pages) that, when displayed, involve multiple objects (e.g., frames). For example, a customer service application at an insurance company may includes files that, when accessed, display web pages having several frames such as an “account information” frame, a “contact information” frame, a “policy claims” frame etc. This organization of the frames is convenient to the application developer because the application modules for different frames can be separately developed then the modules can be reused in multiple pages in any combination. For example, the “account info” frame may occur in every page or just in some of the company's pages. This allows the application developer to rapidly develop complex applications in a modular fashion.
On the downside, requiring the browser to download many independent objects (e.g., frames) to complete a response to a client request can have severe negative impact on performance. In general, each object is requested by the browser independently; therefore, a web page including multiple objects will require several network roundtrips. This causes the impact of network latency to become manifold thereby leading to poor performance.
Other techniques used by application developers can also impact network performance. For example, application developers often implement so-called server-based redirects. A developer may construct an application to comprise several functional modules. When a client requests a URL, a content server may process the URL at a nominal control module which then redirects the client to another module for handling the request. Redirection of client requests can have severe performance impact because each client request must travel the network twice—once to the server's control module and back, and a second time to another (redirected) server module and back.
Network latency can have varying impact on the performance of web and other network applications involving the fetching of an object that in turn requires the fetching of other objects that are external to the originally fetched object. When the latency between the client and the server is small, network latency has limited impact on performance. When the latency is large (e.g., of the order of a second), as is the case when the client and the server are separated by a significant geographic distance, network latency can degrade application performance significantly.
Thus, a market exists for techniques to minimize the impact of network latency on application performance a posteriori to application development. Optimization can be carried out dynamically as a client interacts with an application so that changes to the application (e.g., on the server or client computers) are not required (but may be optional depending on design choice).